Mouse Facility at UC-Irvine provides a variety of services related to making, genotyping, and breeding transgenic, knockout, and other genetically modified mice. It has been operating since 1996 with the goal of facilitating the use of genetically modified mice in research projects by investigators at UCI and the UCI Medical Center. Genetically modified organisms have played a control role in basic biological and biomedical research for many years. Since the development of techniques for modifying the mouse genome in the early 1980's, via DNA microinjection into mouse zygotes and homologous recombination in embryonic stem (ES) cells, genetically modified mice have become a mainstay in a wide variety of fields, including cancer research, genetics, neurobiology, embryology, and pharmacology. Due to its genetic and physiological similarities to humans, and the relative ease of its genetic manipulation, the mouse has become the pre-eminent model organism for studying human diseases, including diabetes, cancer, Alzheimer's disease, and obesity. The annual number of peer-reviewed publications based on genetically modified mice has increased exponentially for the last 15 years. Maintaining the Transgenic Mouse Facility as a shared resource provides a number of advantages to UCI researchers. Although the use of transgenic and knockout mice has become routine, the equipment necessary to generate them remains expensive., and the techniques are not easily mastered. Thus, it is much more efficient and cost-effective to perform such services as microinjection of DNA into zygotes and ES cells into blastocysts in a core facility. Benefits to researchers include lower costs of generating new strains, more reliable completion of projects, and easier entry into field for first time users of transgenic mice.